Users of large amounts of electrical power, such as industrial manufacturing facilities, typically consume such power at uneven rates. During peak periods of manufacturing activity, for example, during normal daylight working hours, such consumers require relatively large amounts of electrical power. During off-peak periods, for example, during night time hours, the amount of power consumed can decrease significantly. Seasonal variations in power consumption are also common. Despite these fluctuating demands for electrical power, electric utilities are required to maintain a generating capacity that exceeds the maximum demand for electricity anticipated during any given period of time. Therefore, electric utilities must maintain generating capacities far in excess of average electrical power requirements in order to meet such occasional and relatively short term demands. The formation and maintenance of such excess capacity is quite expensive, and dramatically increases the average cost of providing electrical power.
In order to better allocate the cost of providing excess power generation capacity to those consumers most requiring such capacity, and in order to encourage such consumers to more evenly distribute their demand for electrical power, the utility rate schedule applied to such consumers is typically divided into two components. The first component is an energy charge which reflects the utility's own energy generation and transmission costs. The charge is typically calculated in cents per kilowatt hour of energy consumed during a particular billing period. The second component is a peak demand charge which reflects the utility's capital costs, and is based on the average energy consumed by the customer during a predetermined demand interval period of time. The peak demand charge is calculated as cents or dollars per kilowatt of actual demand. Such peak demand charges can be quite high as a percentage of the total utility charge over a particular billing period.
Owing to the increased use of peak demand charges by electrical utilities, large industrial consumers of electricity have begun investigating methods for reducing peak power demands from the electrical utility. Load shedding is one approach by which various noncritical electrical loads are automatically removed from a consumer facility's power distribution system during periods of high peak power demand. Peak shaving systems constitute an alternative to load shedding, whereby additional privately-owned generating capacity is utilized to absorb part of the consumer's electrical demand during peak demand times. This can be accomplished by a block approach, in which a local generating system provides all of the power required by certain portions of the consumer's requirements, or by operating a secondary generator in parallel with the electrical utility distribution system. In each of these approaches, the peak power demand recognized by the electrical utility is effectively reduced, thereby reducing the high peak demand charge associated with such power consumption.
Parallel operation of a secondary generating system is particularly advantageous because the electrical consumer can carefully control the amount of secondary power generated to coincide with the most economical operating conditions. Since the basic cost of generating electrical power utilizing a secondary generating system, as opposed to the raw utility cost for generating the same amount of power, is generally much higher, economics dictate that only that amount of power that will reduce the peak demand charges significantly should be produced. The exact equilibrium point varies according to a number of economic factors, for example, the cost of fuel for the secondary generating system, the capital cost for providing the generating system, the actual expected utility power demand during a particular part of the year in a seasonal operation, the actual utility rate structure, and various other factors.
The use of a secondary generating system in conjunction with the utility distribution system is also particularly advantageous for those industrial facilities already employing emergency standby generating systems. In such instances, additional capital expenditure to accomplish peak shaving is minimized because the generating equipment is already in place for emergency use. The same equipment is readily adaptable to the peak shaving application.
Various manufacturers already provide the commercial components necessary to accomplish basic peak shaving. Generator sets of various capacities are available from a number of manufacturers. Many of these generator sets are suitable for parallel utility operation when used in conjunction with appropriate transfer switches and controls. Control equipment supplied with the generator sets can maintain the secondary generator in synchronization with the utility power distribution system, and can control the output of the secondary electrical generator set in accordance with predetermined command signals.
In a typical application of such peak shaving equipment, the actual utility demand by the consumer is sensed and compared to a desired maximum utility demand. In response to the sensed demand exceeding the predetermined maximum demand, one or more generator sets are activated and used to reduce the actual demand to the predetermined demand. This continues until such time as the actual demand cannot be maintained at the predetermined level by the secondary generator, at which time the generator simply runs at full output with the actual utility demand again fluctuating, but offset by the amount of secondary power generated.
Existing systems do not optimize the amount of power produced by the secondary generating system in accordance with economic factors. Instead, such systems merely control to a single predetermined demand setpoint. This has proven to be an inefficient utilization of the secondary generating capacity, owing to the fact that economic factors change frequently according to the time of operation, the cost of fuel, and a number of other factors. In order to most fully realize the advantages of peak shaving, it is necessary to modify the amount of secondary power generated in response to a great number of such factors.
The present invention is directed to overcoming one or more of the problems as set forth above.